β-Lactamases

β-Lactamases are a large structurally heterogeneous familiy of bacterial enzymes catalyzing the cleavage of β-lactam antibiotics that are used as the predominant therapeutics in the treatment of bacterial infections. As β-lactamases appear to be one of the largest problems in human and veterinary infectiological medicine within the next decades and until now no strong pharmaceuticals are known to overcome the β-lactamase mediated bacterial resistances, a great effort of research is required to provide armed weapons against bacterial infections in the future. Therefor our group is working in the area of structure-function research, to get deep insights into structural and kinetical aspects of β-lactamases, which allow the development of new inhibitors. This includes x-ray crystallographic structure solutions and molecular dynmaic calculations, biophysical characterization of enzyme-ligand-complexes as well as the kinetical characterization of beta-lactamases, antibiotics and inhibitors. The following short descriptions give an insight into the current focus of research.

 

The emergence of metallo-β-lactamases (MBLS) represents a real threat to human health since they show a broad spectrum of substrates including carbapenems. Indeed, carbapenems are usually one of the last resort antibiotics for many bacterial infections such as Escherichia coli and Klebsiella pneumoniae. Moreover, despite the huge number of potential molecules already tested, there is currently no clinically useful MBL inhibitor. The fact that some of the MBL genes are plasmid-encoded represents an additional cause of concern. Indeed, they can spread from one strain of bacteria to another by horizontal gene transfer. MBLs are thus now regarded as a therapeutic challenge and the biochemical and structural characterization of this increasingly large MBL family presents a great interest since a detailed study of the active site and of the mechanism of action of these enzymes should lead to the rational design of inhibitors that could be co-administrated with the antibiotic therapy as well as of antibiotics escaping their hydrolytic action.

 

The GES family consists of 18 known variants, all point mutations of the first identified member, GES-1. Although GES-1 was unable to break down carbapenems, subsequent members of the family (e.g. GES-2, GES-5 or GES-14, with an Gly170Asn/Ser substitution) have increasing carbapenemase activity, with the latter enzyme having the dubious distinction of being capable of breaking down all known β-lactams. Production of highly active mutant strains along with horizontal gene transfer commonplace in nature and rampant in hospitals, will continue to give rise to “superbugs” that do not respond to treatment and require the continued development of new drugs.

 

OXA-48-type carbapenem-hydrolysing class D β-lactamases are increasingly reported in enterobacterial species. The enzymes hydrolyse penicillins at a high level and carbapenems at a low level, sparing broad-spectrum cephalosporins, and are not susceptible to β-lactamase inhibitors. Since many OXA-48 producers do not exhibit resistance to broad-spectrum cephalosporins, or only decreased susceptibility to carbapenems, their recognition and detection can be challenging. Adequate screening and detection methods are therefore required to prevent and control their dissemination.